The present invention relates to the fields of power plant engineering, which include the operation of a gas turbine, for example combined cycle power plants. It relates to a method and a device for removing carbon dioxide from the exhaust gas from a gas turbine plant which has a downstream heat recovery process.
A method of this type and a device of this type are known, for example, from document U.S. Pat. No. 5,832,712.
During the increasing discussion of possible climate changes caused by the increase of the carbon dioxide concentration in the Earth""s atmosphere (xe2x80x9cgreenhouse effectxe2x80x9d), which is attributable primarily to the burning of fossil fuels, such as natural gas, mineral oil and coal, there is an increasing range of proposals being put forward as to how, for example in fossil-fired power plants, the carbon dioxide can be removed from the flue gases of the boiler or exhaust gases from gas turbine plants on an industrial scale before it is released into the atmosphere.
One of these proposals is described in U.S. Pat. No. 5,344,627. In this proposal, the flue gas from the fossil-fired boiler of a steam power plant is brought into contact, in countercurrent, with a liquid which absorbs carbon dioxide and contains, for example, an alkanolamine. The carbon dioxide which is absorbed by the liquid is removed from the liquid again at a different point in the liquid cycle and is then liquefied. The liquid cycle together with the necessary absorption and regeneration columns requires a substantial outlay on plant engineering.
Another proposal, which is -known from U.S. Pat. No. 5,665,319, for removing carbon dioxide from a gas which contains carbon dioxide uses, instead of a liquid, a granular metal oxide, which is converted into a metal carbonate by absorbing carbon dioxide and is converted back into the metal oxide by subsequent removal of the carbon dioxide. The granular powder is either conveyed back and forth in a cycle between a fixation tower and a decomposition furnace, or two similar devices with a solid powder bed are used alternately to absorb and release the carbon dioxide by switching between the devices. A drawback of this method is that the device in which the carbon dioxide is released again must in each case be operated as an externally heated furnace.
Finally, in the document U.S. Pat. No. 5,832,712 which is mentioned in the introduction, it is proposed to remove the carbon dioxide from the exhaust gas from a gas turbine plant by bringing the exhaust gas, after it has passed through a heat recovery steam generator, into contact with a liquid which absorbs carbon dioxide in an absorption column. In this case too, there is the drawback of the outlay on plant engineering for the liquid cycle of the absorbing liquid.
Therefore, it is an object of the invention to provide a method and a device which allow simple removal of carbon dioxide from the exhaust gas from a gas turbine plant, the exhaust gas then being subjected to a heat recovery process.
Carbon dioxide is removed at a high temperature level before the heat recovery process and by the use of a rotating, regenerative absorber/desorber, which is equipped with an absorbent coating, for the removal, which absorber/desorber operates between the exhaust gas stream and a separate carbon dioxide cycle.
A first preferred configuration of the method according to the invention is characterized in that heat is transferred from the exhaust gas to the carbon dioxide cycle between the gas turbine plant and the absorber/desorber. In this way, a temperature level which is higher than on the absorption side and is required in order to release the absorbed carbon dioxide in the absorber/desorber is achieved in a simple manner in the carbon dioxide cycle.
The temperature difference between the absorption and desorption sides of the absorber/desorber can be further increased if, according to another refinement of the method, the heat recovery process comprises a water/steam cycle with a heat recovery steam generator, and the exhaust gas, following the heat transfer to the carbon dioxide cycle and prior to entry into the absorber/desorber, is used to superheat steam in the water/steam cycle.
If the temperature of the exhaust gas on emerging from the gas turbine of the gas turbine plant is not sufficient to heat the carbon dioxide cycle, it is expedient to additionally heat the exhaust gas prior to the heat transfer to the carbon dioxide cycle.
Finally, a part stream which corresponds to the carbon dioxide which has been removed from the exhaust gas is branched off from the carbon dioxide cycle and is then cooled.
A preferred configuration of the device according to the invention is distinguished by the fact that a first heat exchanger, which is in communication with the carbon dioxide cycle, is arranged between the gas turbine plant and the absorber/desorber, by the fact that the heat recovery means comprise a water/steam cycle with a heat recovery steam generator, and by the fact that a second heat exchanger for superheating the steam in the water/steam cycle is arranged between the first heat exchanger and the absorber/desorber.
The absorber/desorber is preferably constructed in the manner of a coated regenerative heat exchanger and is equipped with a large reactive surface for the absorption and desorption of carbon dioxide, the core material which bears the coating or an intermediate layer which is arranged between the reactive coating of the absorber/desorber and the core material having a low thermal conductivity in order to reduce the heat transfer between the carbon dioxide cycle and the absorption side.